I'm looking for some online/video tutorials for Blender to follow and I know that Blender 2.63 that just came out earlier this year introduces BMesh, a major overhaul in the Blender modelling system.

I'm worried that if I follow tutorials that use pre 2.63 Blender versions I may start running into things that have completely been changed in 2.63+ (e.g. having to use any special techniques just because ngons weren't possible whereas now they are)

So should I try and find 2.63+ tutorials (are there any?) or am I ok with following tutorials for 2.5/2.6?

As a general rule of thumb, you want tutorials for the version of blender you are using. Sometimes the differences between versions are minor, like between the 2.4x versions, but in the case of 2.4x vs 2.6x, the changes are huge.

The 2.5x series was essentially an intermediate version. Even though it was a precursor to 2.6x, you will find lots of discrepancies.

It is a bit of a chicken & egg situation, but if you are an experienced blender user, you can adapt tutorials for another version or even another product to what you are currently using. But then you are less likely to be watching tutorials, right?

My advice is be aware of the problem but don't worry about it. As you note, BMesh is the big change in 2.6x. If you see differences in the user interface between the tutorial and your blender, then there is a problem and it is time to go look at the release notes and wiki documentation.